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atmospheric pollution for the readings were around the normal level until the 12th day :
the more likely explanation is that the rise in deaths over this period was the beginning
of the intermittent climb to the winter level of mortality—in any case it is in part offset
by the following trough. The second incident, when the readings reached the near smog
level for sulphur and about three-quarters of this level for smoke, may, however, be
considered to be connected with pollution. On the assumption that the peak in
mortality during the period 12—21 November was a consequence of smog, the number
of 'excess' deaths contained therein approximates to about 60—all of them in persons
of 70 + years of age. However, over the same period of the foggy days, as mentioned
earlier, the night-time temperature fell to a low level at or near freezing point and it
could be argued that the rise in mortality, particularly as it affected only the aged, was
as much, or even more, a consequence of this temperature drop than of atmospheric
pollution. It is impossible to say how many of the excess deaths, if in fact excess deaths
did occur, were due to smog and how many to cold. So far, in the history of London
smogs, there does not seem to have been an incident causing excess deaths which has not
also been accompanied by low temperatures. Given a sufficient number of these smog
episodes it may be possible, in due time, to make a statistical estimation of the relative
importance of cold and pollution in their consequences.
To summarise, the protracted fog of mid-November, which never quite attained
the smog pollution level, did not lead to excess deaths of the same order as occur when
the critical level of pollution is reached. The maximum excess was of the order of 60
deaths, all of them among persons aged 70 years or more. It is thought that some, if not
all, the excess deaths may have been attributable to low night temperature.
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